Phonon and Spin Wave Spectra Study on “in situ Oxidizing Sputtered” Ni/NiO Multilayers

An improved sputtering method, which is named “in situ oxidizing sputtering”, was used to prepare periodic Ni/NiO multilayers. Samples studied in this letter contains 20 pairs of Ni/NiO with period about 100Å. In Raman scattering, the low frequency phonon modes are interpreted as LA phonon folding effect, which is usually measured in superlattices with a strict periodic structure. The ferromagnetic resonance spectra were also recorded at room temperature with microwave frequency 9.777GHz. The analysis of spin wave resonance indicates that Ni sublayers are coupled with each other, which is the mechanism that surely relates to the amorphous-like NiO spacers.